Apparatus for and method of truing abrasive screws



Aprilv 5 1927.

B. M. W. HANSON APPARATUS FOR AND METHOD OF TRUING ABRSIVE SCREWS FiledNov. 5o, 192s 4 Sheets-Sheet 1 l! |llllllllllllllllllH d A lllllllllldlll Illlllllllllll'IIIIIIIIIIIIIIIIII Apll l 5 1927 B, M. w. HANsoNAPPARATUS FOR AND METHOD OF TRUING ABRASIVE SCREWS Filed Nov. 30. 1923 4Sheets-Sheet 2 ,4f l @Hoz 1112,11

A ril 5 1927.

p B. M. w; HANsoN APPARATUS FOR AND METHOD 0F TRUING ABRASIVE SCREWSFiled Nov. 50, 1923 4 Sheets-Sheet 5 April 5, 1927. 1,623,113

B. M. W. HANSON APPARATUS FOR AND METHOD. OF TRUING ABRASIVE SCREWS FledNov. 30. 1923 4 Sheets-Sheet 4 l no Patented Apr. 5, 1927.

UNITED' STATES PATENT OFFICE.

BENGT M. W. HANSON, OF HARTFORD', CONNECTICUT; EINAR A. HANSON ANDCLAIR.-I ENCE E. WHITNEY EXECUTORS OF SAID BENGT M. W. HA'NSON,DECEASED.

APPARATUS FOR AND METHOD OF TRUING ABRASIVE SCBEB.v

Application led November 1923. Seria1.No. 677,632.

In' my co-pending application Serial No.l 675,034, filed November 16th,1923, I have shown and described a machine for grinding gears, whereinan abrasive screw ot' emery or the like, and having a helical thread onits periphery, is employed for grinding the teeth of gears in acontinuous operation, the machine being so arranged and constructed thatthe abrasive screw and gear blank are 1H driven at proper relativespeeds with the thread of the abrasive screw meshingA with `the teethonv the blank. The present invention is designed for triling, withprecision, the'tlii'ead on the abrasive screw so that it l5 .will veryaccurately generate the desired form of tooth on a gear blank, forinstance. By the use\of my improved invention, the abrasive screw, whenit has become Worn, may be very expediently and' accurately dressed tothe desired shape. y In the accompanying drawings, I have chown,forillustrative purposes, one vgeneral form of apparatus which I mayemploy in carrying out my invention, but it is to be understood thatthis showing is by way of eX- cmpliticatio'n only and is not to beconstrued as a limitation of the scope of the invention. Quiteobviously, the machine and the methods carried out by the use thereofare susl) ceptible of various modifications, foi-ins yand changes.

The invention accordingly consists in the features of construction,combination of elements and arrangement of parts which will beexemplified in the construction hereinafter Eiet forth, and the scope ofthe application of which will be indicated in the appended claims.

In said drawings:

Figure lis a front View of the machine;

Fig. 2 is a view looking at the left hand end thereof;

Fig. 3 is a view taken substantially on line 3-3 of Fig. 1 and lookingin the direction of Ll l) '45 the arrows Fig. 4 is a top plan view ofthe gearing mechanism;

Fig. v5 is a top plan View, on an enlarged scale, ot the truingmechanism; and

Fig. 6 is a view` similar to Fig. 5 but showing another embodiment oftruing device.

Referring to the drawings in detail, a denotes a base or iixed bed ofany suitable a, for rocking movement about an axis construction on whichis mounted a slide b provided with a bearing e for a spindle d carryingthe abrasive screw c` to be ldressed or retrued. Pivotally mounted o'nthe bifl pre erably parallel to that of the spingle d, is a rocking bedf on which is supported, for

sliding movement longitudinally of the abrasive screw e, a tool carriageg carrying a truing device l1.. .The rocking bed f is provided at itslefthand end with a rearwardly extending arm z' on which ismounted agear box c housing the driving mechanism through which the rocking bedis rocked on.

its fulcrum and the tool carriage g is longi- .tudinally'reciprocated.The truing or resurfacing toolv is hereshown, by Way of example, intheforni of a diamond m, vand this tool is intermittently fedtransversely of the abrasive scrcw through suitable mechanism Zcontrolled by the longitudinal reciprocat-` ing movement of the toolcarriage g'. From the brief foregoing description, it will be understoodthat during the operation of dressing orKretruing the spiral rib orthread on the abrasive screw e, the diamond is vrepeatedly reciprocatedlongitudinally of the abrasive screw in accordance with the lead of thethread thereon, and the diamond is fed towards the abrasive screw eachtime the same is reciprocated so as to operate upon successive portionsof the side facesl of the thread of the screw. In order that` thediamond -m will clear the abrasive screw on its return or inoperativestroke, the rock-y ing bed f is rocked, as hereinafter described more indetail. v In the present illustrative. disclosure of the invention, thework slide Z) is mounted on ways 1()4 on the upper face of the bed a.These ways are at right angles to the axis about which the rocking bedswin s. This slide may be adjusted in any suita le manner, as by meansof a screw 11 (see Fig. 2) which may be turned by a hand wheel 12 on theforward end of a shaft 13, there being provided intermeshing gears 14 onthis shaft and the screw. The spindle d', on which the abrasive screw tobe retrued Ais mounted, may be driven in any suitable manner, as bymeans of a belt (not shown) passing about a pulley 15 fixed to thisspin-dle.

The rocking bed is supported for' rocking movement in any suitablemanner. By way of example, the rocking bed, may be journalled, as shownin Fig. 1, by means of ball bearings 20 on a shaft 21 supported forrotary movement by ball bearings 22 located in suitable brackets 24arisin T from the front corners of the bed a. It wild be understood thatthere will be ball bearing arrangements 20 and 22 at each end of the bedf. The shaft 21, as hereinafter described in detail, is driven fromtheabrasive screw spindle d in order to reciprocate the tool carriage gand rock the bed f in proper timed relation to the rotary movement ofthe abrasive screw. The tool carriage g comprises a main slide 25mounted on ways 26 for reciprocating movement on a line in'parallelisrnwith the axis on which the rocking bed is fulcrumed, and a supplementalslide 27 on the upper face of which is fixed a plate or platform 28 forsupporting the truing device h. The tool carriage g is reciprocated bymeans of a lead screw 29 which is intermittently driven in oppositedirections in proper timed relation with the rotary movement of theabrasive screw e. The supplemental slide 27 may be adjusted on the mainone 25 by means of avscrew 30 in order to properly adjust the diamondlongitudinally of the abrasive screw.

The truing mechanism, as will be seen most clearly from Figs. 2 and 5,includes a table 35 mounted for angular adjustment in a horizontal planeupon the plate 28, and a holder 36 mounted on the table 35 for movementtransversely of the abrasive screw, and, in the present case, at rightangles to the axis about which the table is angularly ,adjustable) Theplate 28 has, at its rear end, a boss 37 (see Fig. 2) forming a bearingwhich receives a stud or pivot pin 38 depending from the forward end ofthe table 35.' On the lower, end of this stud is screwed a nut 39 so asto hold the forward end of the truing device down. For the purpose ofguiding and steadying the table 35, it may -be provided on its underface with an arcuate rib 40 working in an arcuate slot 41, the

center of curvature of which coincides with the axis of the pin or stud38. The forward edge of the lplate 28 is curved, as shown in Fig. 5, andthe table 35 is provided with a gib 42 (see Figs. 1 and 2) whichreceives this edge. The forward edge of the plate 28 is notched, as at43, so as to receive a plunger 44 carried by the table 35. These notcheswill be of such number and so arranged that the tool holder 36 may beindexed to such angular positions that, when this holder is fed stepbystep towards the screw, the dia# mond will be moved at an anglecorresponding to the angularity of the side faces of the thread on theabrasive screw. In the present instance, two such notches are shown,these notches being so located as to permit the diamond to be moved totrue the -a screw or bolt 65.

thread on the abrasive screw, the faces of which are at the usualpressure angle, namely 141/2".

The holder 36, together with the diamond carried thereby, may beintermittently moved in a direction transversely to the abrasive screwin any suitable manner, as by means of a .screw 45 threaded in theholder 36 andent instance, a ratchet wheel 47 is fixed to.

the screw 45, and journalled on the screw is a lever, on one arm 48 ofwhich is pivoted a pawl 49 cooperating with the ratchet wheel 47 Theother arm ,50 of this lever fis connected by a ball and socket joint'51to a rod 52 slidably adjustable in a block 53 connected by a ball andsocket joint 54 to the upstanding leg or arm 55 of a lever 56 pivoted,as at 57, to a plate 58 secured to and movable with the main slide 25 ofthe tool carriage g. Connected to another arm 59 of the lever 56 is afollower pin 60 which is guided, for vertical movement, in a bearing 61provided on the lower end of the plate 58. The lower end of thisfollower pin rides upon a guide member or cam 63 which is in the form ofa plate pivoted, as at 64, for angular adjustment, and adapted to belocked in any desired angular position by The lever 56 is normally urgedin a clockwise direction, in order to maintain the follower pin 60--inengagement with the cam 63, by a spring pressed plunger 66 carried bythe bracket 58 and engaging another arm 67 on the lever 56.

It will be observed that, owing to the ball and socket joints 51 and 54,and, due to the fact that the rod' 52 is longitudinally adjustable inablock 53, provision is made for permitting angular adjustment of thetruing mechanism. It may be assumed that, when the tool carriage g movestowards the right, referring to Fig. 1, the diamond m is moved on itsoperative stroke, that is, it is operating upon the abrasive screw.During this operative stroke, the lever, which carries the pawl' 49,will be moved in a counterclockwise direction, andthe lever 56 will beurged in a clockwise direction to maintain the follower pin 60 inengagement with the guide member 63. When the tool carriage has reachedthe end of its operative stroke, the rocking bed f will be swung on itsfulcrum so as to withdraw the diamond m from the abrasive screw, andthen the tool carriage will be moved to the left, thatis on itsinoperative stroke, and when so moved. the follower pin 60 will ride upthe cam 63, thereby'lmoving the lever 56l counterclockwise, and rotating`the arm 48, which carries the pawl 49, in a clockwise direction. Whenthis pawl is thus (rotated, it will turn the ratchet wheel 47, togetherwith the screw on whichthis wheel is xed, a predetermined amount to feedthe holder 36 and diamond point carried thereby forwardly a very slightdistance;

As stated, it is advisable that on the return or inoperative stroke ofthe dressing tool m, it shall befree of the work. To this end, therocking bed may be rocked in timed relation -with the longitudinalreciprocating movement of the tool carriage. In the present illustrativedisclosure, this is accomplished by means of a cam fixed upon a shaft 76journalled in the gear box which is mounted on the rearwardly extendingarm z' of the rocking bed. Pivoted 'in abracket 77 fixed on the rear endof the arm i is 'a rocking beam 78, the long end or arm of whi restsupon the cam 75 and the other or s orter end or arm of which rests upona pin 79 slidably carried by the bracket 77 and resting upon a suitablev abutment 80 on the fixed bed a. The cam 75 is Aintermittently rotatedthrough 180.

It will beobserved that upon one-half revolution of this cam, theforward end of theA p rocking beam 78 will be lowered, permittin therocking bed to swing rearwardly n n downwardlyl to bring the diamondpoint into operative relation to the abrasive screw.

On the, next half revolution of the cam, which occurs after the diamondpoint has made its operative stroke, the forward end of the beam 78 israised, thereby swin ing the rocking bed in a direction to with raw the4diamond point from operative relation to the abrasive screw so that thediamond point will be clear of the abrasive screw on the return strokeof the former.

The various mechanisms may be driven in any suitable or desiredmanner,but, by way of illustratioinl have shown one form of drive mechanismwhich may be adopted to advantage. The shaft 21 'is driven from theabrasive screw spindle d through 'a worin fixed on this spindle, a wormwheel 86 ont-he shaft 87, and bevel ygears 88 between the shaft 87 andthe shaft 21. The

. upper end. of the shaft 87 is carried by a bearing or housing 89suitably journalled on the spindle d, and one of the bevel gears 88 is slined on the shaft 87 so as to permit of rociing movement 'ofthe rockingbed f and transverse adjustment of the slide b and the parts carriedthereby. Within the gear box c is a shaft 90' which is constantly pdriven from the shaft 21 through the gears .91. Fixed on the shaft 90'isa gear 92 (see Fig. 4) meshing with a gear 93 on the sleevel .94 whichis'normally loose on the shaft 76 which carries 'the reversing cam 75.Fixed screw is the right to the shaft 76 is a cam sleeve 95 which con-4trols the reversing' clutch mechanism for the lead screw through whichthe tool carriage g is reciprocated.

Between the sleeve 94 and the cam sleeve 95 is an escapement ratchetclutch mech` anism through which the shaft 76 is inter-- mittentlyrotated. In the prsent illustrative disclosure, this mechanism includesa ratchet wheel 100 fixe-d to the sleeve 94 and a pawl 101 as at 102, toa disk 103 fixed to the sleeve 95. The pawl 101 is urged into engagementwith the ratchet wheel by a spring pressed plunger 104 carried bythedisk 103. ivoted upon a bracket 105 fixed tothe gear box c are a airof pivoted levers 106 the inner ends o which are diametrically disposedrelative to the ratchet wheel 100, as shown most clearly by dotted linesin Fig. 2. .The outer ends of these escapement levers are, y means ofspring pressed plungers 107, maintained against opposed abutments 108upon a vertlcally movable rod 109 connected at its lower end to a lever110 fixed on a shaft 111 which extends forwardly to the front of themachine. On theforward-end of this shaft is fixed an arm 112 (seeFig. 1) connected by a link 113 to a lever 114 pivoted to the rockingbed. The link 113 may be connected to the lever 114, as shown in Fig. 1,when the abrasive provided with a right hand thread, for instance. If anabrasive screw with a left handv thread is to be retrued, in which caseit may be presumed the tool carriage should bemoved towards the left onits operative stroke, the link 113 would be con. nected to the left handarm 114 of the lever 114. Connected to this lever 114 is a rod115carrying adjustable dogs 116with which to cooperate. f

It will be observed that, when the tool carriage reaches the end of itsoperative stroke, in the present instance, its movement. Itowards theright, referring to Fig. 1, the dog 117 on the tool carriage will strikethe right hand dog 116 thereby moving the rod 115 to and, through theconnections described, rotating the shaft 111 in a direction to lowerthe rod 109. When this rod is thus lowered, theupper escapement lever106 is swung in a direction to release the pawl 101, whereupon this pawlwill engage the ratchet wheel 100 causing the shaft 776 and the cam 75carried thereby to rotate. Rotation of this shaft, however, is limitedto the shaft has made one-half revolution,the pawl 101 strikes the lowerescapment lever 106, whereupon this pawl is disengaged from `the ratchetwheel 100. When the tool carfor, after (see"Figs. 2 and 4) pivoted,

carriage.

115 to the left and, through the connections described, the rod 107 willbe raised, whereupon the lever escapementl lever 106 will be releasedfrom the pawl 101, 'permitting the same to engage the ratchet wheel 100.The

shaft 76'will now be rotated another half revolution and then' the upperescapement lever 106 will disengage the pawl 101 from the ratchet wheel.

The lead screw 29, by means of which the tool carriage is reciprocated,is driven from the shaft 90 in the following manner. Located adjacentthe shaft 90 is a shaft 120 and between this latter shaft and the leadScrew are a train of gears 121. These gears are adapted to be changed sothat the tool carriage may be moved in accordance with the selectedpitch of the thread on the abrasive screw. Fixed on the shaft 90 are apair of gears 122, 123. The gear 122 is in meshnwith a gear 124 loose onthe shaft 120. The other gear 123 drives, through an intermediate gear125 Xed on a stub shaft 126, a gear 127 also loose on the shaft 120.` Itwill be seen that the gears 124 and 127 vare constantly driven 1nopposite directions. The clutch mechanism. for alternately {ixin thegears 124 and 127 to the shaft 120 may ifhe of any suitableconstruction. In the present instance, this clutch mechanism includes asleeve 1284having at each end a single clutch tooth 129. The gears 124,127 ,are respectively provided With a-single clutch tooth 124 and 127adapted to cooperate with corresponding clutch teeth 129 on oppositeends of the sleeve 128. These parts are provided with single clutchteeth-to insure uniformity in the reciprocating movement of the tool Theclutch mechanisnrjust described is controlled by the ratchet clutchmechanism which, in turn, is controlled, as heretofore stated, bythelreciprocating movement of the tool carria e. The sleeve 95 has a camgroove 130 in w lich works a pin 131 carried by a shipper lever 132suitably pivoted on a stud 133. The groove 130has an offset 130 'topermit the lever 132 to be thrown into neutral misitiqn, as by means ofa handle 140 on the upper end of the stud 133. Journalled'on this studis an arm 134 having, in its free end, a -pin 135 which works in agroove 136 in the clutch sleeve 128. One end of the shipper lever 132 isprovided with a pair .of arms between which is positioned a web or rib137 on the arm 134. The arms of the shipper lever 132 carry4 springpressed plungers 138which respectively engage opposite sides of the rib137. The arm 134 is provided in order to prevent iamming of the parts inthe event that,

when the shipper lever is thrown, a tooth on the clutch sleeve 128should strike the top of a tooth on one of the gears 124, 127.

The operation of the mechanism is briefly as follows; When the abrasivescrew\ has become worn to such an extent that it should be retrued, itis secured to the spindle d. With the reversing cam 75 in such positionthat the rocking beam rests upon the lowest point of'this cam, the slideb will be adjusted to move the abrasive screw laterallyy into operativerelation to the diamond point; the truing device will be properlyindexed upon the plate 28 in accordance with the angularity of one ofthe side faces of the thread on the abrasive screw; the supplementalslide 27 of the tool carriage will be adjusted by the screw 30 so as tobring thediamond point into proper relation longitudinally of the threadon the abrasive screw, and the holder 36 will be manually advanced oradjusted by turning the screw to engage the diamond point with the faceof the thread,

preferably, at a `point at the outside edge of this face. Assuming thatthe operative parts of the machine have been properly lselected and setup, the Ymachine may be thrown into operation by turning the handle 140to proper position. The lead screw will now move the tool carriage onits operative stroke during which the diamond point will take a cut onone face of the thread throughout its length. After the tool carriageisA moved to the right to such extent that the diamond point is beyondthey abrasive screw, the dog- 117 on the tool carriage will strike theright hand dog 116 onthe rod 115 whereupon, through the mechanismdescribed, the reversng cam 75 will be rotated 180 to swing the rockinbed upwardly and forwardly and there y withdraw the diamond point fromoperative position and'then the lead screw will be' reversed to -movethe tool carriage on its inoperative stroke. During this inoperativestroke, the cam'or guide member 63 will raise the follower or pin 60 andthereby cause the ratchet mechanism associated with the screw 45 to turnthis screw a very slight amount and thereby feed the diamond point onestep towards the abrasive screw. When.the work carriage has completedits inoperative stroke, the cam 75 will again be rotated 180o whereuponthe rocking bed will swing rearwardly and downwardly to bring thediamond point into operative position with respect to the abrasivescrew, and then the work holder will again be moved on its operativestroke, during which time the diamond point will take another cut in theface of the thread just inwardly of the previous cut. This sequence ofoperations is repeated until one face of v the thread is retruedthroughout its depth.

Then the truing device is angularly adjusted or indexed so that thediamond point will operate upon the other side face of the screw. Theoutside or truncated face of the thread on the abrasive screw may betrued by very slowly moving, by means of the screw 30, the diamond`point in a straight line in In Fig, 6, I have shown, more or lessdiagrammatically, an arrangement of truing mechanism which may beemployed to advantage'when it is desired to true an abrasive lscrewhaving a thread with its side faces other than straight in the directionof their' depth. In this ligure, I have shown the abrasive screw ashaving a thread with 'double curve faces so that the abrasive screw, inoutline, will correspond to a double curve yrack'adapted to mesh withthe double curve gear to be ground. Referring to this ligure, 27designates the supplemental slide of a tool carriage; 28, the platethereon; 35 a table; and 36, a tQol or diamond point holder. In thepresent instance, the tool holder 36 may be moved in a directionlaterally-of the abrasive screw in the same manner as in the precedingembodiment. The screw 45 has a nut 150 slidable in a groove 151 in thebottom of the holder 36 so as to permit this holder to move laterally ofitself under thel inuence of cams 152. These cams, which constitutepattern means, have their operative faces corresponding in all particuars to the shape to be given to the side faces -of the thread on theabrasive screw. The holder 36 is provided with projections 153 whichengage and follow the curved faces of the cams 152. The holder- 36 isurged in a direction to maintain the projections 153 in engagement withthe cams 152 in any suitable manner, as by means of spring pressedplungers 154 carried by the table-35. y.It will be understood that,

with the .arrangement just described, the dia- A mond point, a ter eachoperative stroke 1ongitudinally of the abrasive screw, will be fedslightly inwardly towards the axis of this screw by turning the screw45", and when the diamond point is thus fed inwardly, it will moveslightly longitudinally of the abrasive screw, owing to the cams orpatterns 152. When one face of the thread on the abrasive screw has beentrued up in the manner justtdescribed, the pattern cams 152 are reversedand inverted so that the cam surfaces thereon will take the dotted linepositions shown in this ligure. The other. face of the thread on theabrasive screw may then be retrued. The cams 152 are .diagrammaticallyshown as being held in position by suitable screws 156 and lugs 157.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope-thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a Sense.

I claim as my invention: ,i 1. In combination, means for rotatablysupporting an abrasive screw, a tool for truing therthread on saidscrew, and means for repeatedly and relatively moving said tool andabrasive screw longitudinally of the axis of the latter and inaccordance with the lead of the thread thereon with said tool engagingaside face of said thread at successive points in th'e direction of itsdepth.

2. In combination, means for rotatably supporting an abrasive screw, anddiamond point for truing the thread on said screw movable longitudinallyof. saidscrew in accordance with the lead of the thread thereon andintermittently movable laterally of the screwin accordance with theshape of the faces of said thread. I

`3. In combination, means for rotatably supporting an abrasive screw, atool for truing the thread of said screw, means for repeatedly movingsaid tool longitudinally otthe abrasive screw in accordance with thelead of the thread thereon, and means for intermittently moving saidtool laterally of the screw in accordance with the angularity of theside faces of the thread thereof.

4. In combination, means for rotatably supporting an abrasive screw, adiamond for truing the thread of said screw, means for repeatedly movingsaid diamond longitudinally of the abrasive screw in accordance with thelead of the thread thereon, and automatically actuated means for movingsaid diamond with a step by step movement along the faces of the threadin the direction of their depths.

y5. In combination, means for rotatably supporting an abrasive screw, atool for truing the thread of said screw, means for reciprocating saidtool longitudinally of said screw in accordance with the lead of' thethread thereon, means yfor feeding the tool axially of said screw inaccordance with the shape of the side faces thereof upon eachreciprocating movement of said tool, and

supporting an abrasive screw, a tool for truing the thread on saidscrew, means operatively connected to said spindle for reciprocatingsaid tool longitudinally of the abrasive screw in accordance with thelead Qf the thread thereon, means controlled by the reciprocatingmovement of said tool for intermittently feeding said tool along theface of the thread in the direction of its depth, and means operativelyconnected to said spindle for withdrawing said tool from the abrasivescrew upon the return movement of said tool.

8. In combination, means for rotatably supporting an abrasive screw, a,diamond polnt for truing the thread on said screw mounted for angular.adjustment correspoiding to the angles of the faces of the thread onsaid screw and movable longitudinally of said screw in accordance withthe lead of the thread thereon and laterally of said screw in accordancewith the angles of the side faces of the thread thereon. r

9. In combination, means .for rotatably supporting an abrasive screw, adiamond point for truing the thread on said screw, a holder for saiddiamond point mounted for angular adjustment whereby the same may bemoved at an angle corresponding to the angle of the side faces of thethread on said abrasive screw, means for reciprocating said holder tomove said diamond point longitudinally of the screw in accordance with te lead of the thread thereon, and means for feeding said holder in itsangular positions of adjustment laterally of the abrasive screw.

10. VIn combination, means for rotatably supporting an abrasive screw, atool carriage mounted for rocking movement about an axls parallel to theaxls of said screw, means for reciprocatmg said tool carriagelongitudinally of the scibw in accordance with the lead of the threadthereon, a tool on said tool carriage, means intermittently feeding saidtool on said carriage laterally of the abrasive screw in accordance withthe shape of the faces of the thread, and means actuated in timedrelation to said reciprocating means for rocking said tool carriage towithdraw'th'e tool from the abrasive screw on the inoperative stroke ofthe tool.

11. In combination, means yfor rotatably supporting an abrasive screw,a'rocking bed arranged to swing about an axis parallel to the axis ofthe screw, a tool carriage mount- -ed on said bed for reciprocatingmovement axially of said screw, a tool holder mounted on said carriagefor intermittent feedlng movement transversely ofthe abrasive screw,

and a cam driven in timed relation to the reciprocatin movement of saidcarriage for rocking sai bed to withdraw the tool 'from the abrasivescrew upon the reverse stroke of said tool carriage.

12. In combination, a spindle for rotatably supporting an abrasivescrew, a rocking bed mounted for` swinlging movement about an axisparallel to t e axis of said screw, a tool carriage mounted formovenient on said .rocking b ed axially of said screw, a tool holdermounted on said tool carriage for angular adjustment/in accordance withthe angularity of the ofaces of the thread on said screw, a lead screwconnected to said spindle for reciprocating said tool carriage inaccordance with the lead of the thread on said screw, a cam driven intimed relation with said lead screw for rocking said bed to withdraw thetool on the reverse stroke of said tool carriage, and means controlledby the reciprocating movement of 'said carriage for feeding said toolholder ,laterally of said screw.

13. In combination, means for rotatably supporting an abrasive screw, atool for truing the thread on said screw, means for reciprocating saidtool axially ofthe screw in accordance with t e lead of the thread' thecontour of the side face of the thread in the direction of its depth.

15. In combination, means for rotatably supporting an abrasive screw, atool for truing the thread on said screw, means for reciprocating saidtool longitudinally of said screw in accordance with the lead of thethread thereon, means for moving said tool laterally of said screw witha step by step movement, and pattern means for guiding said .tool whenit ist so moved laterally in conformity to the contour of the side facesof the thread on said screw.

16. The method of truing a thread on an abrasive screw which consists intaking helical cuts in a side face of the thread at successive points inthe direction of its depth.

17. The method of truing a thread on an abrasive screw `which consistsin rotating the screw and repeatedly moving a tool longitudinally of theaxis of the screw'in accordance with the lead of the thread thereon withsaid tool engaging a side face of said thread at successive points inthe direction of its depth.

18. The method of truing a thread on an abrasive screw which consists inrotating the screw, repeatedly reciprocating a resurfacin tool axiallyof the screw in accordance with the lead of the thread thereon, andmoving the tool laterally of the screw with a step movement upon eachreciprocating movement in accordance with the -shape of the side facesof the thread on the screw,

.BENGT M, W. HANSON,

